This application is based upon and claims priority of Japanese Patent Application No. 2001-017477, filed on Jan. 25, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a pupil measurement apparatus, refraction correction apparatus, and pupil measurement method and, more particularly, to a visual function correction apparatus which irradiates a cornea with a laser beam to correct the corneal shape and correct refraction.
2. Description of the Related Art
Conventionally, refraction correction surgeries such as LASIK (LAser in SItu Keratomileusis) are used to correct refraction, in which a cornea is irradiated with an excimer laser to change the corneal shape (e.g., the radius of curvature or distortion), i.e., to change the refracting power of the cornea, thereby correcting the refraction. In LASIK, the surface of the cornea of an eyeball is stripped off thin by an electric knife. Then, the cornea is shaved by irradiating it with an excimer laser. Finally, the stripped corneal surface is returned to the original position, thereby correcting the corneal shape for refraction correction.
For example, near-sightedness occurs because the radius of curvature of a cornea is small, and an image is formed before a retina. To correct the near-sightedness, the cornea is uniformly shaved to increase its radius of curvature, i.e., to make the cornea flatter to correct the visual acuity. Hence, to correct near-sightedness, the cornea is irradiated with a laser beam such that a round laser beam irradiation region is formed.
Additionally, for example, astigmatism occurs because the corneal shape is nonuniform and distorted due to, e.g., the index distribution depending on the elliptical direction of the corneal lens of an eye. To correct the astigmatism, the cornea is shaved to change the radius of curvature at each position of it, thereby correcting the visual acuity.
Hence, to correct near-sightedness including astigmatism when a cornea has, e.g., an elliptical distortion, the cornea is irradiated with a laser beam such that the laser beam irradiation region has an elliptical shape having a major axis perpendicular to the major axis of the elliptical distortion to make the corneal shape uniform.
FIG. 16 is a block diagram showing the arrangement of a conventional refraction correction apparatus which irradiates a cornea with a laser beam to change the corneal shape for visual acuity correction.
Referring to FIG. 16, a cornea 1604 of an eyeball 1603 is irradiated, through a half mirror 1602, with light emitted from an imaging light source 1601. The irradiation light is reflected by the cornea 1604 and supplied to a microscope 1605 and video imaging device 1606 through the half mirror 1602.
The cornea 1604 is enlarged and observed with the microscope 1605. Simultaneously, the image of the cornea 1604 is obtained by the video imaging device 1606, and the obtained image of the cornea 1604 is displayed on a monitor display device 1607.
For, e.g., near-sightedness correction surgery, the operator strips off a thin surface of the cornea 1604 of the patient using an electric knife. Then, the operator observes marks formed on the eyeball (iris) of the patient in advance with the microscope 1605 and aligns the position of the cornea 1604 with the laser beam irradiation position. When alignment between the position of the cornea 1604 and the laser beam irradiation position is ended, the cornea 1604 is irradiated with a laser beam from a laser irradiation device 1608 through the half mirror 1602 to shave the cornea, thereby correcting refraction.
However, when refraction correction surgery is done using the above-described conventional refraction correction apparatus, marks must be formed on the eyeball (conjunctival portion) of the patient, and the position of the cornea 1604 and the laser beam irradiation position must be aligned while checking the marks with the microscope 1605. Hence, the operator requires a skill.
Especially, to correct near-sightedness including astigmatism, the cornea 1604 is irradiated with a laser beam with an elliptical irradiation region in refraction correction surgery. Unless the position of the cornea 1604 and the position of the laser beam are accurately aligned in the direction of rotational axis, the cornea 1604 is not correctly irradiated with the laser beam, and the astigmatism cannot be accurately corrected.
Furthermore, since the eyeball of the patient does not stand still during refraction correction surgery, the laser beam irradiation position and the position of the cornea 1604 shift in the directions of X- and Y-axes and rotational axis. Hence, accurate refraction correction surgery is impossible.
The above problems will be described below with reference to FIGS. 17A, 17B, 18A, and 18B.
FIGS. 17A and 17B are views for explaining the position of the cornea 1604 and a laser beam irradiation position 1701 in refraction correction surgery for correcting near-sightedness. When the position of the cornea 1604 and the laser beam irradiation position 1701 are correctly aligned, the center of the laser beam irradiation position 1701 matches the center of the cornea 1604, as shown in FIG. 17A. Hence, a desired portion of the cornea 1604 can be shaved to accurately correct near-sightedness.
On the other hand, if the position of the cornea 1604 and the laser beam irradiation position 1701 are not correctly aligned, the center of the laser beam irradiation position 1701 shifts from the center of the cornea 1604, as shown in FIG. 17B. Hence, a desired portion of the cornea 1604 cannot be shaved, and consequently, near-sightedness cannot be accurately corrected.
FIGS. 18A and 18B are views for explaining the position of the cornea 1604 and a laser beam irradiation position 1801 in refraction correction surgery for correcting near-sightedness including astigmatism. When the position of the cornea 1604 and the laser beam irradiation position 1801 are correctly aligned, a desired position of the cornea 1604 can be irradiated with the laser beam, as shown in FIG. 18A. Hence, the astigmatism can be accurately corrected.
On the other hand, if the position of the cornea 1604 and the laser beam irradiation position 1801 are not correctly aligned, a desired position of the cornea 1604 cannot be irradiated with the laser beam, as shown in FIG. 18B. Hence, the astigmatism cannot be accurately corrected. Especially, in the refraction correction surgery for correcting near-sightedness including astigmatism, as shown in FIG. 18B, if the major axis of the ellipse to be irradiated with the laser beam does not match the major axis of the elliptical laser beam irradiation region due to the torsion of the eyeball, the astigmatism cannot be accurately corrected, though the position of the cornea 1604 matches the central position of the laser beam irradiation position 1801.
The present invention has been made to solve the above problems, and has as its object to make it possible to accurately measure the position and torsion angle of a cornea without forming any mark on an eyeball to measure the position of the cornea.
It is another object of the present invention to provide a refraction correction apparatus capable of easily and accurately aligning the position of a cornea and a laser beam irradiation position without forming any mark on an eyeball of a patient to align the position of the cornea and the laser beam irradiation position.
According to an aspect of the present invention, there is provided a pupil measurement apparatus comprising an imaging unit for obtaining an image of an eyeball, an arithmetic processing unit for calculating a position and torsion angle of a pupil in the eyeball on the basis of the eyeball image obtained by the imaging unit, and an indicating unit for indicating pieces of information related to the position and torsion angle of the pupil and output from the arithmetic processing unit.
According to another aspect of the present invention, there is provided a pupil measurement apparatus comprising an imaging unit for obtaining an image of an eyeball, an arithmetic processing unit for calculating a position and torsion angle of a pupil in the eyeball on the basis of the eyeball image obtained by the imaging unit, and a storage unit for storing pieces of information related to the position and torsion angle of the pupil and output from the arithmetic processing unit.
According to still another aspect of the present invention, there is provided a pupil measurement apparatus comprising an imaging unit for obtaining an image of an eyeball, a coordinate conversion unit for executing polar coordinates/orthogonal transform processing for the eyeball image obtained by the imaging unit, and an arithmetic processing unit for comparing the eyeball image orthogonally transformed by the coordinate conversion unit with a reference eyeball image stored in advance to calculate a position and torsion angle of a pupil in the eyeball.
A refraction correction apparatus of the present invention has one of the above-mentioned pupil measurement apparatuses.
According to still another aspect of the present invention, there is provided a pupil measurement method wherein an image of an eyeball is obtained, a position and torsion angle of a pupil in the eyeball are calculated on the basis of the obtained eyeball image, and pieces of information related to the calculated position and torsion angle of the pupil are indicated.
According to still another aspect of the present invention, there is provided a pupil measurement method wherein an image of an eyeball is obtained, a position and torsion angle of a pupil in the eyeball are calculated on the basis of the obtained eyeball image, and pieces of information related to the calculated position and torsion angle of the pupil are stored.
According to still another aspect of the present invention, there is provided a pupil measurement method wherein an image of an eyeball is obtained, polar coordinates/orthogonal transform processing is executed for the obtained eyeball image, and pieces of the orthogonally transformed eyeball image is compared with a reference eyeball image stored in advance to calculate a position and torsion angle of a pupil in the eyeball.
According to the present invention with the above arrangements, on the basis of an obtained eyeball image, the position and torsion angle of a pupil in the eyeball are calculated, and pieces of information related to the calculated position and torsion angle of the pupil are indicated or stored. Hence, the position and torsion angle of a cornea can be accurately measured by executing arithmetic processing for the eyeball image obtained from the eyeball without forming any mark on the eyeball to measure the position of the cornea or pupil in the eyeball.
Additionally, on the basis of the obtained eyeball image, the pieces of information related to the calculated position and torsion angle of the pupil are indicated or stored. When the pupil measurement apparatus is used for a refraction correction apparatus, the position of the cornea and the laser beam irradiation position can easily be accurately aligned.